I haven't used mTurk personally, but I know people who have, and I've looked a lot into their model.
Here's the deal: For a small amount of money (1 to 5 cents, or more if you like), you can pay people to take a specific action on your site, like posting a review, voting on 10 items, commenting to a post, etc.
- Look at 25 photos and click on the parts that are sidewalk ($0.02)
- Enter the title, name, and residence of a US Patent ($0.08)
- Write a 30-word comment to a blog post ($0.03)
- Find the longitude and latitude of a business, given its street address ($0.10)
- Write a one-paragraph abstract of an information technology article ($0.05)
I find it amazing that so many people are willing to do such drudgery-laden, time-intensive tasks, but evidently, when you toss a bunch of nickels into the air, lots of people jump.